Safety explosive line cutter



March 1, 1960 R. B. 'THORNESS 2,926,565

SAFETY EXPLOSIVE Lmmumm Filed March- 10 1958 luvtw'roa RUDOLPH B.THoRNEss ATTYS 9 Claims. (Cl. 89-1) This invention relates to equipment-release devices, and

is concerned more particularly with electrically fired explosive devices for severing lines such as the load line of a high altitude balloon. v i

The pending patent application of Bohl et al. Serial No. 676,451, for a Blast-Free Explosive Line Cutter discloses among other thing a bullet formed of cup- I, like members having knife-edge rims and arranged with their closed ends abutting the respective faces of a disc gasket, so that there is a rim at each end of the bullet. Thus either member may be the forward member in the barrel and serve as the means to cut the load line.

On occasion this type of device has failed by reason of the fact that the explosion pressure expanded the rim portion of the rear cup-like member into such tight engagement with the barrel that the rear member froze to the barrel and thus the forward member was not impelled, so that the line was not cut. This failure is believed to have been due to oxidation of the rear rim from being on the shelf a long time.

It is a salient object of the invention to provide a safety explosive line cutting device which is free of the foregoing fault.

Another object is to provide a more reliable inexpensive lighter weight safety explosive line cutter.

Further objects and advantages of the invention will appear as the description proceeds.

The invention will be better understood upon reference to the following description and the accompanying drawing, wherein:

Fig. 1 is an elevational view of a line cutting device constructed in accordance with the invention.

Fig. 2 is a left end elevational view of the same.

Fig. 3 is a view in section and elevation of the device shown in Fig. 1, with parts of an electric circuit shown schematically.

Fig. 4 is a sectional view taken at 44 in Fig. 3, the line being omitted.

Fig. 5 is a face view of the seal at the left, before the wiring is passed therethrough.

Fig. 6 is similar to Fig. 3 but shows the device after it is fired.

Fig. 7 is a sectional view taken at 7'7 in Fig. 6.

Fig. 8 is a schematic view showing the cutting device assembled with the load line of a balloon.

Referring more particularly to the drawing, disclosing an illustrative embodiment of the invention, there is shown generally at 1% a line cutting device having a case 12 comprising a barrel 14 and end caps 16 and 18. The barrel 14 may be a piece of standard iron pipe, that is, pipe stocked by dealers and readily purchasable and in common use in plumbing and for other consumer and industrial purposes, such as water or gas pipe, formed with an eye 20 comprising diametrically opposite holes 22 and the communicating barrel bore 24, for the passage of a line, such for example as a balloon-anchoring, ballast-supporting, or load line 26. The caps 16 and 18, which are preferably standard pipe caps, that is, pipe threaded pipe ends 28, the cap 16 having a hole 30. i

A bullet indicated generally'32 is disposed in the bore 24 between the cap 16 and theeye 20, and comprises a cup-like knife 34 having a knife-edge rim 36in snug sliding engagement with the bore wall 37, a pair of spaced disc gaskets 38 and 40 in snug sliding engagement with the wall adjacent the closed end or base 42 of the knife, and a driver disc or spacer 44 fitting loosely in the bore and positioned between the gaskets. The disc 44, although shown coaxial with the barrel 14, may of course in practice engage the bore wall 37 by gravity and thus be eccentric to the barrel, without loss in 'efficiency. A squib 46 extends in the bore 24 between the cap 1 6 and the gasket 38. Wiring 48 from the squib 46 is tightly embraced by the walls of a slit 50. formed in a gasket seal such as the Washer 52 adjacent the inner surface 54 of the base of the cap 16 and thence passes through the cap hole 30 and forms; part of an electric circuit including a switch 56 and a battery 58 (Fig. 3). The base 60 of the cap 18 provides a stop for arresting the flight of the impelled bullet 32, and the axial distance from the stop to the rearmost parts 62 of the eyeholes 22 is in such relation to the length of the bullet that when the bullet is fired and stopped its gasketing blocks access of the explosion gases and fragments to the eyeholes (Fig. 6).

. The several gaskets are preferably made of Neoprene or other suitable elastomeric material, and the knife34 and spacer 44 are formed of drill rod or other suitable material.

The line 26 is adapted to pass through the eye 20 and engage in'theeyeholes ZZ with a friction fit so as to support the'device 10. V

On closing of the switch 56, the squib 46 is fired, impelling the bullet 32 so that the gaskets 38 and 40, particularly the latter, are compressedinto gas-tightengagement with the bore wall 37 as indicated at 64, the cutting edge 36 slices the line 26 at the ends of the line portion 66 withinthe bore,and the forward end ofthe cutting member 34 impinges against and is upset as at 68 by the base 60 of the cap 18, with the line slice 66 trapped (Fig. 6). This upsetting absorbs part of the shock of impact. Inasmuch as the gaskets 38 and 40 remain at the rear of the eye 20 after impact, these gaskets block access of the gases and squib fragments to the eye. At the same time, the seal '52 is forced tight about the wiring 48 and tight against the annular inner surface 54 about the cap hole 30 so as to block access of the gases and fragments to the cap hole. Thus no gas or fragment can escape from the device 10, which is of suflicient strength to preclude rupture by the explosion. The device 10 accordingly cuts the line 26 yet prevents the line from catching fire.

The device 10 is sometimes used to sever a line on or near the ground, as, for example, the ground anchor line (not shown), to launch a balloon. In such a case launching personnel or balloon equipment near the device 10 are protected by the safety features of the device against injury.

Pipe of a given commercial size may vary somewhat in inside diameter and roundness from batch to batch. The cutter rim 36 is initially formed to an oversize diameter so that it will not pass freely into the barrel 14. The base 42 is inserted in the forward end 70 of the barrel i4. Then the knife 34 is rammed rearward farther into the barrel 14, the thin knife-edge 36 yielding to enter the barrel and conform to the cross-sectional-shape of the barrel bore wall 37 and engage the wall with the friction needed to hold the knife in the desired position (Fig. 3) preparatory to firing. The gaskets 38 and 40 are some what oversize to insure a. snug friction fit with the wall of the bore and are preferably inserted with the spacer 44 from the other end of the barrel 14.

The sealing function adjacent the eye 20 is performed primarily by the gasket 40. The primary function of the gasket 38 is to cooperate with the gasket 40 in holding the spacer 44 from falling out of the barrel 14 before the other parts are assembled with the barrel.

An illustrative installation of the invention 'is shown schematically in Fig. 8, wherein the load line 26 from a balloon envelope 72 extends through and friction'a'lly supports a cutting device below which the line sus pends a parachute 74 and a gondola 76 which may include among other things meterological and telemetering equipment and the switch 56 and battery 58.

While a preferred embodiment has been described in some detail, it should be regarded as an example of the invention and not as a restriction or limitation thereof as changes may be made in the construction and arrangernnt of the parts without departing from the spirit and scope of the'inv'ention.

I claim:

I. In a safety explosive line cutting device, a barrel having a pair of holes forming with the barrel 'bore a transverse eye to receive a line, a bullet in the bore and rearward of the eye and adapted to be impelled forward, a squib at the rear of the bullet, the bullet comprising a front member having a rear end of slightly less diameter than the bore and a line-shearing edge frictionally engaging the bore wall, a rear member of slightly less diameter than the wall, elastomeric means substantially softer than said front and rear members and disposed between the members and in a position to be squeezed by the members into gas-tight engagement with the wall in response to the pressure of the explosion gases pursuant to firing of the squib, a stop for terminating the flight of the impelled bullet and arranged to arrest the bullet on shearing of the line, the axial distance from the elastomeric means to said eye being at least equal to the length of the bullets flight so that the squeezed elastomeric means will block access of the gases to the eyeholes when the bullet is stopped, and elastomeric means frictionally engaging the wall and engaging the rear member and cooperating with said edge and the wall in retaining the members in closely assembled relation and preventing their gravitation along the barrel before the squib is fired.

2. The structure of claim 1, characterized in that the 4 two elastomeric means are discrete parts and the rear member is sandwiched between them.

3. The structure of claim 2, characterized in that the two elastomeric means are interchangeable.

4. The structure of claim 2, characterized in that the rear member and the two elastomeric means are discs.

5. The structure of claim 1, characterized in that the edge is of greater diameter than the remainder of the front member.

6. The structure of claim 1, characterized in that the squib is entirely rearward of the bullet.

7. In a safety explosive line cutting device of the character described, a bullet comprising front and rear members, the front member having a deformable annular front radially outwardly projecting feather edge, the rear member being a disc, the rear end of the front member being flat and of substantially the same diameter as the rear member, an elastomeric element substantially softer than said front arid rear members and sandwiched between the rear member and the rear end of the front member, and a second elastomeric element, the rear member being sandwiched between the elastomeric elements, said edge and elements being ofsubstantially the same normal diameter and of slightly greater diameter than the rear member, so that the bullet can be forced into a barrel bore of a diameter slightly less than said normal diameter and greater than the rear member diameter, and when the bullet is in the bore, said edge and elements will yield and frictionally engage the bore wall and retain the members and elements in closely assembled relation and against gravitating along the barrel.

8. The structure of claim 7, characterized in that the elastomeric elements are interchangeable.

9. The structure of claim 7, characterized in that the bullet comprises only the members and elements.

References Cited in the file of this patent UNITED STATES PATENTS 1,899,925 Brofelth Mar. 7, 1933 2,073,609 Court Mar. 16, 1937 2,129,875 Rost Sept. 13, 1938 2,346,494 Leland Apr. 11, 1944 2,581,645 Frieder et al. Jan. 8, 1952 2,616,748 Hight Nov. 4, 1952 2,700,336 Sillitto'et al. Jan. 25, 1955 2,755,550 Benjamin July 24, 1956 

